Influences of Geographic Environment - Ellen Churchill Semple (libby ebook reader .TXT) 📗
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The chief effect of a varied relief is a varied climate. This changes with altitude in much the same way as with latitude. Heat and absolute humidity diminish, generally speaking, as height increases, while rainfall becomes greater up to a certain level. The effect of ascending and descending currents of air is to diminish the range of temperature on mountain slopes and produce rather an oceanic type of climate. The larger and more uniform a climatic district, the more conspicuously do even slight elevations form climatic islands, like the Harz Mountains in the North German lowlands. A land of monotonous relief has a uniform climate, while a region rich in vertical articulations is rich also in local varieties of climate.1254 A highland of considerable elevation forms a cold district in the Temperate Zone, a temperate one in the Tropics, and a moist one in a desert or steppe. Especially in arid and torrid belts does the value of elevation for human life increase.
The highlands of Mexico, South America and the Himalayan rim of India show stratified zones of tropical, temperate, and arctic climate, to which plant, animal and human life conform. The response is conspicuous in the varying density of population in the successive altitude zones. Central Asia shows a threefold cultural stratification of its population, each attended by the appropriate density, according to location in steppe, piedmont and mountain. The steppes have their scattered pastoral nomads; the piedmonts, with their irrigation streams, support sedentary agricultural peoples, concentrated at focal points in commercial and industrial towns; the higher reaches of the mountains are occupied by sparse groups of peasants and shepherds, wringing from upland pasture and scant field a miserable subsistence. The same stratification appears in the Atlas Mountains, intensified on the southern slope by the contrast between the closely populated belt of the piedmont and the wandering Tuareg tribes of the Sahara on the one hand, and the sparse Berber settlements of the Atlas highlands on the other. The long slope of Mount Kilimanjaro in German East Africa descends to a coastal belt of steppe and desert, inhabited by Swahili cattle-breeders. Its piedmont, from 1000 feet above the plain up to 2400 feet, constitutes a zone of rich irrigated plantations and gardens, densely populated by peaceful folk of mingled Bantu and Hamitic blood. At 6000 feet, where forests cease, are found the kraals, cattle, sheep and goats of the semi-nomadic Masai of doubtful Hamitic stock, who raid the coastal lowlands for cattle, and purchase all their vegetable food from the tillage belt.1255 [See maps page 105 and 487.]
Density Of Population In Italy.
Density Of Population In Italy.
This stratification assumes marked variations in the different geographical zones. In Greenland life is restricted to the piedmont coastal belt; above this rises the desert waste of the ice fields. Norway shows a tide-washed piedmont, containing a large majority of the population; above this, a steep slope sparsely inhabited; and higher still, a wild plateau summit occupied in summer only by grazing herds or migrant reindeer Lapps. Farther south the Alps show successive tiers of rural economy, again with their appropriate density of settlement. On their lower slope is found the vineyard belt, a region of highly intensive tillage, large returns upon labor, and hence of closely distributed settlement. Above that is the zone of field agriculture, less productive and less thickly peopled. Higher still is the wide zone of hay farming and stock-raising, supporting a sparse, semi-nomadic population and characterized by villages which diminish with the altitude and cease beyond 2000 meters. On Aetna, located in the tropical Mediterranean, three girdles of altitude have long been recognized,—the girdle of agriculture, the forest belt, and the desert summit. But the tourist who ascends Aetna, passes from the coast through a zone of orange and lemon groves, which are protected by temporary matting roofs against occasional frosts; then through vineyards and olive orchards which rise to 800 meters; then through a belt of summer crops rising to 1550 meters, and varied between 1400 and 1850 meters elevation by stretches of chestnut groves, whose green expanse is broken here and there by the huts of the forest guards, the highest tenants of the mountain. From these lonely dwellings down to the sea, density of population increases regularly to a maximum of over 385 to the square mile (150 to the square kilometer) near the coast.
In the tropical highlands of Mexico, Central and South America, on the other hand, concentration of population and its concomitant cultural development begin to appear above the 2000 meter line. Here are the chief seats of population. Mexico has three recognized altitude zones, the cold, the temperate and the hot, corresponding to plateau, high slopes and coastal piedmont up to 1000 meters or 3300 feet; but the first two contain nine-tenths of the people. While the plateau has in some sections a population dense as that of France, the lowlands are sparsely peopled by wild Indians and lumbermen. Ecuador has three-fourths of its population crowded into the plateau basins (mean elevation 8000 feet or 2500 meters), enclosed by the ranges of the Andes. Peru presents a similar distribution, with a comparatively dense population on a plateau reaching to 11,000 feet (3500 meters) or more, though its coastal belt, being healthful, dry, and fairly well supplied with irrigation streams from the Andes, is better developed than any other similar district in tropical America.1256 In Bolivia, 72 per cent of the total population live at an altitude of 6000 to 14,000 feet, while five out of the nine most densely peopled provinces lie at elevations over 11,000 feet.1257 [See map page 9.]
From Mexico to central Chile, the heavy rains from the trade-winds clothe the slopes with dense forests, except on the lee side of the high Andean wall of Peru and Chile, and reduce much of the piedmont to malarial swamp and jungle. The discouragement to primitive tillage found in the unequal fight with a tropical forest, the dryer, more bracing and healthful climate of the high intermontane basins, their favorable conditions for agriculture by irrigation, and their naturally defined location stimulating to early cultural development, all combined to concentrate the population of prehistoric America upon the high valleys and plateaus. In historic times these centers have persisted, because the civilized or semi-civilized districts could be best exploited by the Spanish conquerors and especially because they yielded rich mineral wealth. Furthermore, the white population which has subsequently invaded tropical America has to a predominant degree reinforced the native plateau populations, while the imported negroes and mulattoes have sought the more congenial climatic conditions found in the hot lowlands.
The relativity of geographical advantages in different historical periods warns us against assuming in all times a sparsity of population in mountains, even when the adjoining lowlands offer many attractions of climate and soil. In ages of incessant warfare, when the motive of safety has strongly influenced distribution of population, protected mountain sites have attracted settlement from the exposed plains, and thus increased the relative density of population on the steep slopes. The corrugated plateau of Armenia and Kurdistan, located on the uneasy political frontier of Russia, Persia and Asiatic Turkey, exposed for centuries to nomadic invasion from the east, shows a sparser population on its broad intermontane plains than on the surrounding ranges. Security makes the latter the choicer places of residence. Hence they are held by the overbearing and marauding Kurds, late-comers into the land, while the older and numerically weaker Armenians cower down on the lower levels.1258 Here is an inversion of the usual order. The militantly stronger intruders, with no taste for agriculture, have seized the safer and commanding position on the hills, descending in winter with their cattle and horses to pasture and prey upon field and granary of the valley folk, whose better soil is a questionable advantage.
Instances of this sort, rare in modern times, because of of general economic and social progress, multiply when we go into the history of primitive or ancient peoples. The Cherokee Indians of the Southern Appalachians, surrounded by powerful neighbors in the Chickasaws, Creeks and the encroaching whites of the seaboard colonies, attacked by war parties of Shawnees and Iroquois from the north, located the bulk of their nation in the mountains. The Overhill and Middle towns, numbering together thirty-three and situated wholly in the mountains, comprised four-fifths of their fighting force in 1775, while the nine towns distributed in the flat lands of Georgia and South Carolina were small and unimportant. The Indians themselves distinguished these two divisions of their country, the one as Otarre or mountainous, and the others as Ayrate or low.1259 Similarly in ancient Gaul the three strongest tribes, the Sequani, Aedui, and Arverni, all had a large mountain nucleus. The Sequani held the Jura range with part of the Saône Valley; the Aedui held the northeast corner of the Central Plateau and some lands on the Saône, while the Arverni inhabited the western and central portion of the same highland. In a period of constant tribal migrations and war, the occupants of these high, protected locations were better able to defend themselves, and they maintained an adequate food supply by holding some of the adjoining lowland. Archaeologists generally agree that in central and southern Italy settlement first took place in the mountains, gradually extending thence down into the plains. The superiority of the upland climate, the more abundant rainfall, the greater security against attack offered by mountain sites, and the excellent soil for agriculture resulting from the geological make-up of the Apennines, all combined to draw thither primitive and later settlement.1260 [See map page 559.] Similarly in Britain of the Bronze Age, before the peoples of Aryan speech began to swarm over the island, the primitive inhabitants, involved in constant clan or tribal warfare, placed their villages on the hills, and left in the indestructible terraces on their slopes the evidences of a vanished race and an outgrown social order.1261
The advance of civilization, which brought the ancient pirate-ridden city from the inner edge of the coastal zone down to the wave-washed strand, also drew the hill town down to the plain, and the mountain population from their inaccessible strongholds to the more accessible and productive valleys. These facts contain a hint. The future investigation of archaeological remains in high mountain districts may reveal at considerable elevations the oldest and hence lowest strata of prehistoric development,
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